<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title> 伸缩性</title>
    <style>
        .outer {
            width: 400px;
            height: 400px;
            background-color: grey;
            display: flex;
            margin: auto;
            flex-basis: 10px;
        }
        .inner {
            width: 100px;
            height: 100px;
            background-color: orange;
            border-width: 2px;
            border-style: solid;
            border-color: black;

        }
        .inner2 {
            flex-basis: 300px;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner">1</div>
        <div class="inner inner2">2</div>
        <div class="inner">3</div>
    </div>
</body>
</html>
</body>
</html>